CHAP, v.] DEEP-SEA SOUNDING. 207 



is required, as in coast-surveying, it is necessary to 

 sound from a boat, which can be kept in position by 

 the oars and reference to some fixed objects on shore. 

 This ordinary system of sounding answers perfectly 

 well for comparatively shallow water, but it breaks 

 down for depths much over 1,000 fathoms. The 

 weight is not sufficient to carry the line rapidly and 

 vertically to the bottom ; and if a heavier weight be 

 used, ordinary sounding line is unable to draw up its 

 own weight along with that of the lead from great 

 depths, and gives way. No impulse is felt when the 

 lead reaches the bottom, and the line goes on running 

 out, and if any attempt be made to stop it it breaks. 

 In some cases bights of the line seem to be carried 

 along by submarine currents, and in others it is 

 found that the line has been running out by its own 

 weight only, and coiling itself in a tangled mass 

 directly over the lead. All these sources of error 

 vitiate very deep soundings. In many of the older 

 observations made by oflS.cers of our own navy and 

 of that of the United States, the depth returned 

 for many points in the Atlantic we now know to 

 have been greatly exaggerated; thus Lieutenant 

 Walsh, of the U.S. schooner ' Taney,' reported a cast 

 with the deep-sea lead at 34,000 feet without 

 bottom;' Lieutenant Berryman, of the U.S. brig 

 'Dolphin,' attempted unsuccessfully to sound mid- 

 ocean with a line 39,000 feet long;^ Captain 

 Denham, of H.M.S. 'Herald,' reported bottom in the 



' Maury's Sailing Directions, 5tli edition, p. 165, and 6tli edition 

 (1854), p. 213. 



2 Maury, Physical Geography of the Sea. Eleventh edition, 

 p. 309. 



